In display devices such as flat panel displays or projectors, which have been significantly expanded in recent years, an optical element containing a large number of microstructures having a lens function or a light-scattering function is provided in front and in rear of each pixel to transmit a larger amount of light to realize a brighter image. In micro-total analysis devices, chemical synthesis devices, and fluid-controlling systems, each employing a MEMS, a microstructure is formed on a surface of glass, and the microstructures are joined with each other, to fabricate a liquid flow path or various analytical reaction system. For such a purpose, a glass material excellent in optical characteristics and chemical stability is expected to be used. However, processing employing a semiconductor process such as dry-etching has a low processing efficiency for the glass material. Therefore, an efficient processing method for fabricating a three-dimensional microstructure is expected to be developed.
As a method for fabricating a large amount of three-dimensional microstructures at low cost, micromolding technology employing a molding die is promising. As illustrated in FIG. 1, the micromolding technology is for replicating a profile by pressing a molding die against a material to be molded at a temperature which allows the material to be molded to be softened. In the case where the material to be molded is a resin material, the processing is possible at a relatively low temperature. For this reason, the micromolding technology has already been spread for a large number of devices. Further, the profile can be replicated with nanometer-order accuracy in the molding employing the die. Therefore, such micromolding technology has been actively developed as nanoimprint technology (see Non-Patent Literatures 1 and 2 and Patent Literature 1).
Increase in area of molding is also an important issue for increasing a speed and an efficiency of a molding step. However, if the area to be molded at one time is increased, a necessary load is proportionally increased. Therefore, a pressure means is extremely increased in size, which in turn results in remarkably increased size of a molding apparatus. In addition, it becomes difficult to uniformly apply a pressure to a region to be molded. In order to solve these problems, a load means employing a fluid as a medium (see Patent Literature 2) and a method for scanning the entire area to be molded with a pressure head which is relatively small as compared with the area to be molded (see Patent Literature 3) have been developed.
For the molding of the glass substrate by employing the micromolding technology as described above, a molding process at a higher temperature is required because the glass material has a higher softening temperature than that of the resin material. The use of low-melting-point glass as the molding material allows a process temperature to be lowered to a certain degree (see Non-Patent Literature 3). However, there is a problem that various additive elements contained in the low-melting-point glass affect optical performance or chemical stability. Though a process and an apparatus which enable the molding at a high temperature have been developed for molding high-melting-point glass (see Non-Patent Literature 4), the molding apparatus is required to have several heat-shielding structures or heat-insulating materials to realize the high-temperature process. Thus, there is a problem that the apparatus is increased in size. Moreover, the glass requires a larger pressure for molding as compared with that required for the resin material, and hence means for applying a large load is required. Therefore, there also arises a problem that the apparatus becomes large. Further, in order to prevent the molding die from degrading in the high-temperature molding and to prevent poor molding due to gas confinement, the molding is required to be performed in a vacuum, which becomes another factor of the increase in size of the apparatus.
On the other hand, the high-temperature molding requires a long time for heating and cooling, and hence the molding over a large area is important for improving the efficiency of the molding step. However, a weight uniformization means using the fluid as the medium or the like cannot be used at a high temperature. Moreover, the application of the scanning method with the pressure head is also difficult in view of heat shield of the entire mechanism and the accommodation of the mechanism in a vacuum chamber. Therefore, for molding of the glass material over a large area, the apparatus becomes extremely large in size and expensive.
Further, a burden imposed on the molding die becomes large in the molding under the conditions of a high temperature and a large load. Thus, the cracking of the molding die also becomes a problem.                [Non-Patent Literature 1] “Nanostructure Fabrication by Nanoimprint Technology” by Hirai, Journal of the Japan Society for Precision Engineering, vol. 70, No. 10, 2004, pp. 1223-1227        [Non-Patent Literature 2] “Nanoimprint Technology” by Miyauchi, Kuwahara and Ogino, Journal of Japan Institute of Electronics Packaging, vol. 7, No. 6, 2004, pp. 497-500        [Non-Patent Literature 3] Y. Hirai, K. Kanakugi, T. Yamaguchi, K. Yao, S. Kitagawa, Y. Tanaka, “Fine pattern fabrication on glass surface by imprint lithography”, Microelecron. Eng., Vol. 67-68, 2003, pp. 237-244        [Non-Patent Literature 4] “Large-Area Micro-Hot Embossing of Glass Materials with Glassy Carbon Mold Machined by Dicing” by Takahashi and Maeda, Journal of the Japan Society for Technology of Plasticity, vol. 47, No. 549, 2006, pp. 963-967        [Patent Literature 1] JP-A-2006-269919 (“JP-A” means unexamined published Japanese patent application)        [Patent Literature 2] JP-A-2006-326927        [Patent Literature 3] JP-A-2007-19451        